With reference to FIG. 1, a conventional inductive position sensor, shown generally indicated at 10, includes a source coil 12, a first sensing coil 14, a second sensing coil 16 and a moving target 18. The target 18 can be any material which generates eddy currents, but is preferably aluminum since it is inexpensive and readily available. The purpose is to decrease the efficiency of induction due to eddy currents, which is useful in position sensing. FIG. 2 shows the amplitude of the AC output of sensing coil 14 in the shape of a Sine wave at 20, while the amplitude of the AC output of sensing coil 16 is shown in the shape of a Cosine wave at 22. The Sine and Cosine output of coils 14 and 16 can be combined in an arctangent (A Tan 2) calculation to produce the linear response (line 24) to the position of the target 18. This response is largely independent of the air gap and scalar amplitude.
These conventional inductive position sensors are often complex circuits that require compromise in design for many reasons, including available space in the body of the application, or often constraint of the position of the wires themselves on the PCB as they coil and lap over one another. The constraints and compromises often lead to imperfections in the linearity or offset of the transfer curve of position and output.
This problem is currently solved with offset coils (additional loops outside of the circuit which can influence the offset), or by introducing internal loops to help mitigate some of the non-linearity. Many ASIC configurations incorporate slope and offset modification software to assist with these issues, when no mechanical solution is possible (often due to mechanical constraints). Unfortunately, offset coils require a significant amount of additional board space, and that is not always available. Software solutions require expensive, higher end components, or a reduction in resolution to retain room for error compensation.
Thus, there is a need to influence the offset and linearity of the transfer curve of an inductive position sensor without the use of offset coils or software.